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Selective Breeding Introduction

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Selective Breeding Introduction

Read the farm scenario, then use evidence to explain how people select inherited traits. Selective breeding can create useful traits, but it can also have costs.

A Farm’s Breeding Plan

A farmer wants corn plants that produce large ears. Each season, the farmer saves seeds from plants with the largest ears and grows them. The next generation varies: some plants produce large ears, while others produce smaller ones. The farmer again saves seeds from the largest-ear plants. Over many generations, large ears become more common. This is selective breeding: people use a planned process to choose parents based on inherited traits. It is different from natural selection, in which environmental conditions affect which organisms survive and reproduce.

1.Which choice best defines selective breeding?

Organisms change traits because they decide to
Humans choose organisms with desired inherited traits to reproduce
All organisms in a population become identical in one generation
An environment directly gives an organism a new trait

2.In the farm scenario, what trait does the farmer want, and which plants are chosen as parents for the next generation?

3.Put the breeding plan in order by numbering each event from 1 to 4: plants grow; seeds from selected plants are saved; plants with the desired trait are chosen; a new generation grows from the saved seeds.

4.Why might large ears become more common after the farmer repeats this process for many generations?

Choose the Trait

A dog breeder wants dogs with a calm temperament. Two healthy dogs are selected because they are calm, and some of their puppies are calm too. Other puppies are more energetic. A trait that is inherited can be passed from parents to offspring, but offspring do not always inherit the exact combination of traits their parents have.

5.True or false: Every puppy from two calm parents is guaranteed to have a calm temperament. Explain your choice.

6.Match each example to the trait people are selecting: (1) dairy cows chosen as parents because they produce more milk; (2) tomato plants chosen as parents because their fruit ripens later; (3) dogs chosen as parents because they have the desired coat type. Traits: A. fruit that ripens later; B. higher milk production; C. a particular coat type.

1. Dairy cows
2. Tomato plants
3. Dogs

A. Fruit that ripens later
B. Higher milk production
C. A particular coat type

7.Which action is an example of natural selection rather than selective breeding?

A farmer saves seeds from the tallest plants
A breeder pairs dogs with a desired coat color
In a drought, plants that tolerate dry conditions survive and produce more seeds
A gardener chooses tomato plants with larger fruit

8.In the farm scenario, what step does the farmer repeat each season, and how can repeating it affect the population over time?

9.Selective breeding can have a trade-off. For example, selecting only for a very particular appearance may reduce genetic variation. Why could reduced variation make a population more vulnerable to a new disease or environmental change?

10.A farmer wants tomatoes that ripen later so they can travel to stores without becoming too soft. Describe a two-step selective breeding plan and name one possible trade-off the farmer should monitor.